1. Technical Field
This disclosure relates to a power control system and a power control method, especially to a power control system and a power control method for an embedded controller in a computer device.
2. Description of Related Art
There are increased number of global and regional regulations relating to the power management of electronic devices with the improvement of people's consciousness of environmental protection. The electronic device manufacturers are devoted to develop more energy-saving products without sacrificing the performance thereof while complying with the regulations. For portable products like notebook computers and mobile phones, less power consumption means prolonged usage time and standby time and could be a powerful feature.
According to the latest “advanced configuration and power interface (ACPI)” specification (which is an open standard for device configuration and power management by the operating system) published in year 2011, five power states are defined for an ACPI-compliant computer device.
S0: Working, where monitor is off but background tasks are running
S1: All processor caches are flushed, and the CPU(s) stops executing instructions. Power to the CPU(s) and RAM is maintained, while devices that do not indicate they must remain on may be powered down.
S2: CPU is powered off, while other devices are powered on.
S3: Commonly referred to as standby, sleep, or suspend to RAM that still remains powered.
S4: Hibernation or Suspend to Disk. All content of main memory is saved to non-volatile memory such as a hard drive and is powered down.
S5: Soft Off. No previous content is retained, so a full reboot is required. Other components may remain powered so the computer can “wake” on input from the keyboard, clock, modem, LAN, or USB device.
As described above, an “inactive” computer device may be in the suspend-to-RAM state, the suspend-to-disc state, or the shutdown state.
Besides, according to the “directive of eco-design requirements of energy-using product (EuP)” regulated by European Union, the electronic products sold in all member states should have a power consumption of no more than 0.5 watts in the off state as of Jan. 7, 2013. For a computer device in the off state, the mainboard therein and the power supply adapter (AC adapter) for example are even energy-consuming. Therefore, it is preferable for a mainboard to have a power consumption of 0.25 watts to leave a margin for the power supply adapter.
In the state-of-the-art, an embedded controller in the computer device, though in the shutdown state, is still energy-consuming. The embedded controller serves to control peripheral input/output accessories of the computer device like keyboards, computer mice, touch pads, compact-disc recorder, universal serial bus (USB), etc., when the computer device is started or switched off. The embedded controller is generally powered by a switching power supply circuit which can offer more than 90% of the power conversion efficiency if the load current is large enough. Besides, the use of the switching power supply circuit is beneficial to facilitate the design of the heat dissipation device of the computer device. However, when the load current is relatively small, for example only several milli-ampere, the power conversion efficiency of the switching power supply circuit may be worse than that of a linear regulator. Thus, the power consumption ratio of the embedded controller to the entire computer device is relatively significant when in shutdown state.